What size sprocket should I get?

[FurryOnTheInside]

I get a lovely workout on my 66cc MB. I put more effort into pedalling it than my regular bicycles, because I am having more fun, because I am going fast and I know that I have a choice of pedalling or not, and the trip won't take too long. I'm not thinking about the two hours of mandatory pedalling at a boring speed. I have a road touring triple chainset on the front and a mtb nine speed cassette on the hub, so I can pedal along with the engine up to about 36-37mph, then the engine has to do it all by itself.

I would think a 40T or 41T would be about right for a 26" wheel mountain bike.
Personally I wouldn't worry about engine capacity as the cops would have to disassemble the engine to measure the displacement.

The batteries for an ebike with a 30mph cruising speed will be expensive a.f. and generally/ usually/ nearly always have to be bought separately from the E motor kit. This is something that seems to get overlooked.

 

[FNTPuck]

On my mountain bike with a basically stock slant head 66cc(just drilled exh baffle and NGK plug) w/ stock 44t sprocket I can pedal along with it at 25mph cruising speed. I do it more for fun since it doesnt NEED the pedal assist with the 44t, but I like to do it after slowing down for turns or going up hills.

I haven't tried any higher than that since it is still in break-in and I am limiting its abuse, but with another gear or two left I could likely do 30 and still pedal.

On the single speed Hyper frame with 41t rear and a bunch more mods the pedals are useless after like 15mph unless you can move your legs like the Flash

 

[Will'smotobikes19]

40 t is pretty good its smaller than a 44 but still has some torque It's what's on my 79cc bike.

 

[Old Busted Hotness]

If I wanted to go 25mph but pedal as though I am going 10mph what would my options be?

That's kind of a strange case, but to do it you'd want to change the pedal-side sprockets. Or start out with an 18- or 21-speed bike. Then you can pedal in top gear, and be able to shift down when you need to.

 

[bakaneko]

The batteries for an ebike with a 30mph cruising speed will be expensive a.f. and generally/ usually/ nearly always have to be bought separately from the E motor kit. This is something that seems to get overlooked.

This generally depend on the length of the trip. The OP is only going 8 miles one way with a desired speed of about 25 mph. He can recharge at work. This requirement is not that bad to meet on a tighter budget. But, if you wanted to say go 30 mph for 20 mile commute then yes this will be expensive to do.

 

[Old Busted Hotness]

That's kind of a strange case, but to do it you'd want to change the pedal-side sprockets. Or start out with an 18- or 21-speed bike. Then you can pedal in top gear, and be able to shift down when you need to.

And more on that: If you're going to use a multi-speed chainring, you'll want a 2-stroke or electric. 4-strokes are just too wide unless you use a rack mount.